1. Technical Field
The present invention relates to a radio communication base station.
2. Background Art
A wide-ranging communication enable area is required in mobile communication services for cellular phones or the like. In a building or an underground shopping center, however, an electromagnetic wave reaching distance becomes extremely short because of a structure of a building. Thus, an electromagnetic wave dead zone is easily created.
In such a place, to reduce the dead zone of mobile communication, generally, many base stations or antennas must be installed (e.g., refer to Patent Document 1).
FIG. 1 is a diagram showing a conventional method of covering a dead zone. As shown in FIG. 1, a configuration of a conventional example uses abase station device 301 of CDMA (Code Division Multiple Access) or the like, a duplexer (DUP) for transmitting transmission signals input to/output from the base station device 301 by sharing one path, a plurality of adding/branching filters (H) for synthesizing or branching the transmission signals input/output by the duplexer (DUP), and a plurality of antennas 302 connected to the plurality of hierarchically connected adding/branching filters (H).
First, the duplexer (DUP) combines radio signals input to/output from the base station device 301 through one high-frequency cable. Next, the radio signals are multiple-branched through the adding/branching filters (H), and connected to the plurality of antennas 302. Conventionally, dead zones have been reduced by installing the antennas 302 in the different dead zones. In another conventional example, dead zones have been reduced by individually installing compact base station devices in the dead zones.
However, according to the method shown in FIG. 1, power of the radio signals is reduced by the adding/branching filters (H) in proportion to the number of branches. To compensate for the reduction in power, extremely large power supply has been necessary for the base station device 301.
Additionally, for example, there is a loss in the midway of a path from the base station device 301 to the antenna 302. Thus, large transmission power supplied from the base station device 301 has directly caused a large power loss.
Furthermore, according to the method of individually installing the base station devices 301 in the deal zones, a modulation/demodulation unit, a base band unit, a common unit, or the like relatively large in circuit size and power consumption must be installed in each dead zone. Thus, with this configuration, the system has become extremely large as compared with the configuration of FIG. 1.
Patent Document 1
JP 08-505503 A